1. Field of the Invention
The present invention relates to a multi-layer light guide apparatus, more particularly to the light guide apparatus made of two or more layers light-guide materials, the apparatus provides better light output and less lost by arranging the layers from greater refractive index to smaller.
2. Description of Related Art
Light guide plate serves as a medium for guiding incident light into a display backlight module. Most backlight modules are the edge types. Through the light guide plate, the edge-lighting type backlight guides the lateral light out of the front surface of display, and therefore enhances the panel's luminance and average brightness.
The theory of the light-guide plate is to guide the incident light to the other end of the plate. In particular, a specific structure of one side of the light-guide plate causes light diffusion at various angles. Therefore, the incident light may be guided to output from the plate's front surface. The bigger refractive index allows the higher capability of the light guiding. Furthermore, the other paths of light may be guided into the light-guide plate with respect to a reflective plate on the bottom of the plate besides the front light.
U.S. Pat. No. 5,594,830 introduces a double-layer light guide plate. Reference is made to FIG. 1 showing a schematic diagram of a wedge-shaped optical device.
A wedge-shaped optical device 10 is shown. Main structure thereof is composed of a wedge layer 13, a transparent layer 18 and a structural layer 17 adhered thereto. A light from the source 12 reaches a lateral side. This type of light source 12 entering the wedge-shaped optical device 10 may often be a pipe-shaped device.
The material of the wedge-shaped optical device 10 results in a critical angle θC which results in a full reflection. The light firstly enters a wedge layer 13 of the light-guide device 10, and forms a light path 14. The light then propagates into the structural layer 17 through a transparent layer 18. Full reflection is formed on the surface of structural layer 17. The light then propagates to the structural layer 17 through the transparent layer 18. After process of refraction and reflection, an emitting light 19 is formed after out of the wedge-shaped light-guide device 10.
Nevertheless, the critical angle for each layer of the light guide device may be changed between the two layers. Therefore, conventional device causes energy loss of the up-refractive light due to defective design. For example, a full reflection may be caused at a certain angle and stop the light out of the device.